lp:~cjwatson/storm/is-and-is-not-operators

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Merged into lp:storm at revision 577

Andrey Fedoseev (community): Approve on 2022-10-19

Diff: 233 lines (+173/-0)

3 files modified

NEWS (+1/-0)
storm/expr.py (+70/-0)
storm/tests/expr.py (+102/-0)

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577. By Colin Watson on 2022-10-18

Add storm.expr.Is and storm.expr.IsNot operators.

Launchpad has had custom `IsTrue` and `IsFalse` operators for a while,
because there are a few places where `expr` or `expr == True` (or the
equivalents for False) don't quite do what we need: for example, if
you're working with a nullable boolean column, then SQL NULL semantics
mean that `expr = TRUE` or `expr = FALSE` return NULL when `expr` is
NULL, which can be undesirable at times.

In addition, `==` and `!=` comparisons with True/False/None are
typically picked up as errors by modern linters, since in normal Python
code they should use `is` or `is not` or simple boolean tests instead.
Having to override this is an annoyance.

Compare
https://docs.sqlalchemy.org/en/20/core/operators.html#identity-comparisons,
although SQLAlchemy is more permissive; it seems to be happy to compile
anything on the right-hand-side of `IS` or `IS NOT` and leave it up to
the database. Since we already have to take some care with how booleans
are rendered, and there's no guarantee that the spelling of `IS TRUE`
etc. is going to match the way that boolean values themselves are
spelled, I thought it better to limit the set of right-hand-side
expressions that we will compile.

I've checked that current versions of all the databases currently
supported by Storm (PostgreSQL, MySQL, and SQLite) support all the
resulting expressions, although in the case of SQLite it does need at
least version 3.23.0 (released in 2018).

576. By Colin Watson on 2022-03-17

[r=ilasc] Clarify exception for a property with allow_none=False and default=None.

575. By Colin Watson on 2021-12-14

[r=cjwatson] Fix a typo in the tutorial doctest code block

574. By Colin Watson on 2021-05-25

[r=ilasc] Fix test compatibility with MySQL >= 8.0.24.

573. By Colin Watson on 2021-05-14

Bump version to 0.25.0.99.

572. By Colin Watson on 2021-05-14

Avoid traceback reference cycles when wrapping exceptions. [r=ilasc]

571. By Colin Watson on 2021-04-19

Release Storm 0.25.

570. By Colin Watson on 2021-04-19

Fix MANIFEST.in prune syntax.

569. By Colin Watson on 2021-04-19

[r=ilasc] Support Python 3.9.

568. By Colin Watson on 2021-04-15

[r=ilasc] Restore MySQL support.